Liquid crystal display (LCD for short) device is the electronic product with the greatest developing potential in display field, and has the advantages of low driving voltage, low power consumption, light in weight, small in size, no radiated harmful rays, and the like.
The liquid crystal display relies on an anisotropic surface processing of substrate surface films (i.e., alignment layers) to obtain various arrangements of liquid crystal molecules, and the alignment of liquid crystal molecules is one of the key technologies in liquid crystal display. Generally, a rubbing process is used to form a pattern, which enables that the movement of the liquid crystal molecules is oriented, on a surface of a substrate which forms a liquid crystal cell, such that the liquid crystal molecules on the surface of the substrate form an arrangement in order with respect to the substrate. Therefore, the liquid crystal molecules exhibit an order in long-range at macro level, so as to realize the image display.
As shown in FIG. 1, in a conventional display substrate an alignment layer 3 is only disposed in a display area 1, but not disposed in a non-display area 2. Therefore, roughness of surface is different between the display area 1 and the non-display area 2. This difference of roughness of surface leads to the following problems: in a rubbing process, degrees of wear to rubbing cloth are different between the display area 1 and the non-display area 2, such that the conditions of rubbing cloth corresponding to respective areas are different. Therefore, when a rubbing cloth, which is in poor conditions due to a long time rubbing with the non-display area 2, is rubbing the display area 1, it will produce imprints, such that Mura defect such as surrounding blocks, V blocks, H blocks, and the like occurs on the display area 1. On the other hand, metal wirings, which are connected to external circuits, are further disposed on the non-display area 2. Therefore, there may be some metal residuals on the surface of non-display area 2 besides the metal wirings. The presence of the metal residuals results in that the rubbing cloth, which is used for the non-display area 2, has a relatively larger amount of the electrostatic charges and hence is easier to absorb small foreign matters. By comparing the colors and conditions of different rubbing cloth, it may confirm that the small foreign matters have fell into a display substrate, that is, it is possible to leave the foreign matters in the cell, and thus a defect of bright dot is occurred.
In practices, it has been confirmed that the Mura defect is a severe quality problem. The Mura defect severely affects image quality of a product and hence the pass rate of the electrical testing (ET) is low, resulting in serious wasting of materials and equipments in back-end and quality problems. Furthermore, the foreign matters in the cell lead to broken bright spots on the whole screen when the light is turned on, this also severely affects the product quality. These two defects are more evident in small size display substrates. Accordingly, these two defects are the technical problems that need to be solved urgently in the field of display technology.